Paper making machinery produces a web of paper. It is known to trim side edges of the web. It is known in the art to cut the trim using a blade, such as a rotary blade, or using a water jet. An overview of trim handling systems is described in the article, “Trim Handling Systems” presented at the TAPPI Papermaking Conference, Atlanta, Ga., 1999.
As described, trim conveying systems may be divided into five categories as follows:
1) a system for discharging the trim directly into a repulper below the winder,
2) an injector system,
3) a chopper fan system,
4) a combination shredder and transport fan system, and
5) a vacuum system.
Even in case (1) where the repulper is immediately below the winder area, the trim material is removed from the web using a duct or chute and a source of negative pressure to draw the trim into the duct or chute. The trim material is typically guided into the pulper of the paper making machine and immediately returned into producing paper.
Some paper making machines have web speeds well above 60 km/h, and in fact as high as 100 km/h to 140 km/h. At such speeds, a number of problems arise in edge trimming, for example, the stability of the web due to air turbulence, as is described in commonly-assigned PCT publication WO 2011/121390.
One such problem is the starting of trimming. When an untrimmed web is already in motion on the machine, the introduction or insertion of the cutting tool could disturb the web in a negative way. In some cases, bringing the tool in from the outside could cause the outer side edge to fold up. If the tool is brought down onto the web from above or below, not only must care be taken not to cause too much resistance on the web and crumple the web, but the trim must be carefully separated from the trim downstream of the cutting tool to allow the trim being cut from the web to go into duct or chute for recovery. If this separation is not done properly, the stability of the web can be jeopardized.
The separating of the trim can be done on slow webs by hand, however, this is not the case for high speed webs. It is known in the art to use a water jet system to separate the trim when the trimming tool engages the web. This typically involves using a number of small water jets placed across the trim width that are pulsed to cause a break in the trim (and not in the web). In the case of a water jet trim tool, the jet is positioned over the web, and the jet is turned on to begin the trim cutting. Very shortly thereafter, the separation of the trim from itself ensues.
The guiding of the trim into a handling chute, shaft or duct is done in paper making machines by connecting the duct to a source of suction. The flow rate of air drawn for such operation is considerable.
Applicants have used in a trim handling duct an air amplifier jet, at the outlet of the duct in an upper part of the repulper, to create a negative pressure in the duct to draw trim along the duct. The same system used additionally a pair of conical air jets to push trim into the inlet of the trim handling duct.